It has been well known for a number of years to convert heat to electricity through the use of thermionic converters wherein an electron emitter is heated to a sufficiently high temperature so that it emits electrons into the surrounding space. An electron collector is located in juxtaposition to the electron emitter and is maintained at a substantially lower temperature so that the electrons being emitted are received by the juxtaposed collector. The space between the emitter and the collector is usually filled with a very low pressure gas, such as cesium vapor, e.g. pressure of about 50 to 1300 Pa, in order to reduce the space charge and the work function of the emission of electrons. An electrical circuit between the collector and the emitter is completed through an external load, through which an electrical current will flow.
Early thermionic converters were generally of the single cell type, e.g. U.S. Pat. Nos. 3,215,868 and 3,218,487; many of these were intended for use with nuclear reactors. However, multi-cell thermionic converters were also developed several decades ago; for example, U.S. Pat. No. 3,702,408 shows a multiple cell arrangement that employs a central heat pipe which can be filled with a vaporizable heat transfer fluid, such as sodium, to uniformly heat its interior. Emitters are carried on the exterior heat transfer surface of the central heat pipe, juxtaposed with surrounding collectors, and a segmental type of approach is used to build a conversion apparatus of substantial length, e.g. 8-10 cells in length. U.S. Pat. No. 4,667,126 shows a totally different multicell arrangement where a plurality of electron collectors are attached to a flat wall of electrically insulating material.
U.S. Pat. No. 4,755,350 discloses a thermionic energy conversion system wherein fissionable nuclear fuel surrounds cylindrical arrangements of thermionic emitter electrodes, which in turn circumscribe collector electrodes disposed about a central heat sink that may contain a material, such as lithium hydride, which can absorb heat through phase change.
U.S. Pat. No. 5,219,516 discloses a thermionic electric converter designed for use in a nuclear reactor application where heat will be furnished to the exterior of a generally cylindrical heat pipe through which heat flows inward to an emitter of tubular shape. It emits electrons radially inward that are collected by a juxtaposed tubular collector mounted on a heat transfer pipe that effects transfer of heat axially therefrom to a heat sink in the form of a set of remotely disposed cooling fins.
U.S. Pat. No. 5,459,996 shows a thermionic converter arrangement which is part of a spacecraft 5 and which includes a black body receiver 30 designed to effect thermal storage of solar energy received via a pair of mirror assemblies 50. Conceptually shown are a plurality of radially disposed conversion devices 42 that would convert the stored heat energy to electrical power when an insulation sleeve 40 is retracted.
Although the prior art shows various types of multicell thermionic converters, including designs that may be adaptable to applications in outer space, improved designs are continuously being sought, along with methods for more efficiently and more economically making such multi-cell thermionic converters.